The wireless industry is increasingly focusing on high quality of service, which is a competitive advantage for a wireless service provider. Quality of service may be viewed in terms of network coverage, speech quality, network accessibility, and the number of dropped calls.
To achieve optimal network coverage and performance, wireless cellular carriers, must know the signal strength, interference and data throughput (capacity) at all locations of their network coverage areas. The current capacity test of cellular networks is accomplished with sophisticated drive test equipment that utilizes high-performance scanning receivers. The scanner receiver is typically integrated into a test system comprised of a GPS Receiver (location and time), devices that make and break connections, dedicated hardware for data collection, and a vehicular antenna. A laptop typically serves as the dedicated hardware.
The vehicle travels a predefined route while the scanner receiver collects signals from the antenna and performs protocol-specific measurements. The system transfers the measurement data, together with GPS time and position information, to the laptop or dedicated hardware for display and storage. After a single or a series of drive tests, the logged measurement data may be uploaded to a PC or server for analysis (e.g., post-processing). Application-specific software transforms the drive-test data into a user-friendly format, utilizing maps, graphics, and statistical functions.
The metrics determined from drive test data may be combined with metrics acquired by other scanners or with metrics determined at a different time to provide a picture of the health of the network.
Drive tests provide highly accurate and detailed data regarding the state of a network. However, a drive test is a time consuming exercise that captures data along a specified test route. The serial nature of drive tests results in data being captured at different times. A large network may require drive tests to be taken over several hours or even days.
The data that results from the drive tests provide a significant amount of specific data about the channel characteristics. Understanding the channel characteristics allows for manipulation of the phase and amplitude of each transmitter in order to form a beam (or beams, either in physical space or in vector space (virtual beam/beams)). To correctly form a beam (or beams), the transmitter uses knowledge of the characteristics of the channel. One approach to determining channel characteristics is to send a known signal (reference signal (RS) in LTE) to a mobile device (a user equipment or “UE” in LTE terminology). The mobile device then sends back the channel quality indicator (CQI) measures to the transmitter. The transmitter applies the correct phase and amplitude adjustments to form a beam directed at the mobile device. For beamforming, it is required to adjust the phases and amplitude of each transmitter. However, the CQI feedback from UEs is only with regards to the serving base station sector.